Is this the spike point or round point Bismark?
If it is the spike point, you need to really pay attention to that spike. Some who shave with a spike purposely dull the tip so that they don't have to worry about it so much.
Also, keep your pressure as light as possible. The straight will usually only cut if you are running the blade parallel to the edge, or with a spike point if you use too much pressure (which isn't much at all) on the tip.